Customarily, the folding of a set of up to perhaps 30 or so sheets in a stitcher/folder machine results in the finished product having a spine with a convex end surface and sheets having a distinct outward bow adjacent the spine. This means that the booklet tends to open out, giving it a less attractive appearance, and also makes it more difficult to stack a number of the booklets for storage and transportation purposes because they will not lie “flat”. One cannot stack a large number of such booklets all with the spine on the same side, because the stack becomes lop-sided. One has to stack the booklets with some spines on one side and some on the other, in order to equalise the stack.
GB-A-2360013 describes a method of treating a booklet of sheets folded to create a curved spine, and an apparatus for carrying out the method. A folded booklet is clamped adjacent its spine between clamping jaws which extend along the length of the spine and have respective longitudinal ribs which engage the booklet adjacent the spine. The booklet is fed through the jaws into a position in which it abuts a stop plate and a portion adjacent the spine protrudes beyond the jaws. The final position is determined by the stop plate. After withdrawal of the stop plate, a forming means is passed along the length of the protruding portion to flatten the curved spine of the booklet.
Whilst perfectly satisfactory from many points of view, the apparatus and method of GB-A-2360013 is subject to the disadvantage that it can be relatively slow in operation and can be limited in the thickness of the booklets it can process.